Microscopic examination of animal cells typically involves first taking a sample of body fluid consisting of a relatively large quantity of fluid and very few cells. To facilitate examination of the cells it is necessary to remove them from the fluid and collect them in concentrated form.
Typically cells are separated from the fluid by placing the cell-containing fluid in a glass or plastic container similar to a common test tube, and then placing the container in a receptacle of a centrifuge which when rotated causes the cells to move to the outer end or bottom of the container. The fluid is then decanted away leaving a concentration of cells and some fluid in the bottom of the container. Then a small amount of a mucilaginous substance, such as agar, is placed in the container and the mixture of cells and the substance is again centrifuged. This second centrifuging results in a "button" of the substance with a concentration of cells in its bottom surface. The button is then removed from the container and the excess substance is carefully trimmed away. The trimmed button is mounted in a paraffin block which is then sliced in cell-thick sections suitable for mounting on a microscope slide.
Removing the button from the container is a delicate procedure. It is normally done with a wooden applicator and quite often the button is broken up. The button, or what is then left of it, is placed in an enclosure called a "cassette" consisting of rectangular upper and lower parts having slots or holes in their major faces. The cassette containing the trimmed button is then soaked in an appropriate solution to prepare the trimmed button for mounting in the paraffin block.
There are several distinct disadvantages to this prior art procedure. One disadvantage is the necessity for decanting the fluid while the cells are still suspended in the lower levels of the fluid resulting in the possibility of some cells being lost or the uniformity of the concentration of the cells being diminished during the decanting. Another disadvantage is the necessity for centrifuging twice. Another is having the cells on the bottom of the button with no means for removing the portion containing the cells without danger of disruption of the button.
This invention overcomes these disadvantages by using a lower cassette portion which generally can be placed in a fixed position adjacent to the bottom of the fluid container and which has upwardly extending projections which facilitate its removal from the container. The inner cavity of this lower part of the cassette is shaped to receive a button of a mucilaginous substance. The lower cassette part with the button placed in its cavity is first fitted into the bottom of the container and then the body fluid is poured into the container. During centrifuging the cells adhere to the top surface of the button permitting the fluid then to be easily poured away without disturbing the cells. The lower cassette part holding the button and adhered cells is then removed by means of the projections which are then detached. The upper cassette part is then attached to the lower cassette part and the normal procedures of soaking etc. are followed.
The benefits of the present invention thus lie primarily in totally eliminating the disadvantages of the prior art devices and procedures described above. Other benefits and advantages will become apparent to those skilled in the art from the following description of presently preferred embodiments of the invention and from the accompanying drawings.